The present invention relates generally to a zoom lens and an imaging apparatus using the same, and more particularly to a zoom lens that is more downsized for use with imaging apparatus inclusive of video cameras and digital cameras.
In recent years, imaging apparatus such as digital cameras designed to take images of subjects using solid-state imaging devices such as CCDs or CMOSs in place of silver-halide film cameras have became mainstream. Further, they have now a wide spectrum of categories from the commercial high-end type to the compact low-end type.
Users of such low-end type digital cameras would enjoy snapping shots over a wide range of scenes at any time in any place. For this reason, preference is now given to small-format digital cameras, especially the ones of the type that can be well put away in the pockets of clothing or baggage, is convenient to carry around, and is slimmed down in their thickness direction.
On the other hand, the compact type digital cameras have had generally a zoom ratio of the order of 3. Now, however, there is a growing demand for digital cameras having a zoom ratio higher than ever before.
For zoom lenses that can have relatively high zoom ratios, there is a zoom lens known in the art, which is of the type that comprises, in order from its object side, a first lens group of positive refracting power, a second lens group of negative refracting power, a third lens group of positive refracting power and a fourth lens group of positive refracting power, wherein the spacing sandwiched between the respective lens groups is changed to change the focal length.
Of such zoom lenses, those having a relatively reduced number of lenses and favorable for size and cost reductions are known from Patent Publications 1 and 2.
For instance, Example 3 of Patent Publication 1 shows a zoom lens made up of a total of 8 lenses: two lenses for the first lens group, two lenses for the second lens group, three lenses for the third lens group, and one lens for the fourth lens group.
For instance, Examples 2 and 3 of Patent Publication 2 show a zoom lens made up of a total of 8 lenses: two lenses for the first lens group, three lenses for the second lens group, two lenses for the third lens group, and one lens for the fourth lens group.
Of camera dimensions, the thickness direction size is primarily determined by a lens barrel; to slim down the camera, it is effective to slim down the lens barrel.
In more recent years, general use has been made of the so-called collapsible mount type where, when the camera is in use, the lens barrel is unfolded from within the cameral body, and when it is not in use, the lens barrel is folded down in the camera body. For this reason, there is a demand for a zoom lens that takes care of the slimming-down of the lens barrel upon received at a lens mount.
So far, zoom lenses used with imaging apparatus such as digital cameras and video cameras have had to meet the requirements for high angles of view, high zoom performance, weight and cost reductions, as is the case with general cameras.
For instance, among zoom lenses suitable for solid-state imaging devices like CCD or CMOS sensors, there is a zoom lens known, which comprises a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power and a fourth lens group having positive refracting power, and which is slimmed down in the thickness direction upon received at a lens mount while working for making sure the desired zoom ratio.
The zoom lens shown in Patent Publication 3 is favorable for zooming from the wide-angle end to the telephoto end, because a high-refractive-index glass material is used for a negative lens in the second lens group thereby making sure the second lens group has negative refracting power.
[Patent Publication 1]
JP(A)2001-133687
[Patent Publication 2]
JP (A) 9-184982
[Patent Publication 3]
JP(A)2006-171055
However, these prior zoom lenses have a zoom ratio of at most about 3.
In view of such problems as described above, the invention provides a zoom lens which can easily make sure the desired zoom ratio even with a reduced number of lens components, works for size reductions upon received at a lens mount, and can easily make sure the desired optical performance.
The problem with the glass lens shown in Patent Publication 3 the second problem to be solved by the invention is that lens surface processing costs much, and when the lens surface is processed into an aspheric surface, the fabrication cost soars more.
According to the second aspect of the invention, the aforesaid second problem is solved by the provision of a four- or more-group zoom lens easily capable of making sure the desired zoom ratio, in which the second lens group is easily fabricated at low costs.
Further, the invention provides a zoom lens easily capable of making sure the desired optical performance while keeping fabrication costs low.
Still further, the invention provides an imaging apparatus comprising such a zoom lens.